Why only consider negative features in backward push?

[wzfhaha]

For the BackwardPush function in base.h, the code seems only perform backward push only for negative features.

GBP/precompute/base.h

Line 154 in f811fc2

double old = negativeFeature[w][ik];

[wzfhaha]

Another question, the code actually adopts BiPPR as the propagation rule, which is not consistent with the paper.

GBP/utils.py

Line 24 in f811fc2

features = BiP.ppr(datastr,alpha,rmax,rrz)